CHICAGO (Reuters) - An increase in the number of foodborne
illnesses caused by contaminated spinach or lettuce over the
past 35 years cannot be explained by increases in salad
consumption over the same period, U.S. government researchers
said on Monday.

They said the findings reinforce the need for local, state
and federal health authorities to monitor preparation of leafy
green vegetables from the point of harvest all the way through
the food preparation process.

"Consumption of leafy greens has increased over the years,
but it does not completely explain the increase in the
proportion of foodborne outbreaks due to leafy green
consumption," Dr. Michael Lynch, a researcher with the U.S.
Centers for Disease Control and Prevention, said in a
statement.

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A spate of high-profile food safety scares in the past two
years raised concerns among consumers, Congress and federal
health regulators about the safety of the U.S. food supply.

Prompted by E. coli outbreaks linked with spinach and
lettuce in 2006, Lynch and colleagues set out to study past
outbreaks and see if some patterns could emerge.

"We wondered whether it was just related to more people and
more people eating more leafy greens," Lynch said in a
telephone interview.

Using CDC data, Lynch's team analyzed more than 10,000
disease outbreaks reported between 1973 and 2006. They
presented their findings on Monday at the International
Conference on Emerging Infectious Diseases in Atlanta.

They found about 5 percent of outbreaks were related to
leafy greens. About 60 percent of those were caused by the
norovirus, which causes "stomach flu," but 10 percent were
caused by Salmonella bacteria and 9 percent were caused by E.
coli 0157, a dangerous strain of the usually benign bacteria.

They found the number of cases of disease linked to leafy
greens far outpace increases in salad consumption.

U.S. leafy green consumption rose 17 percent during
1986-1995 compared with the previous decade, but outbreaks of
foodborne disease caused by leafy greens increased by 60
percent in that period.

In the 1996-2005 time frame, leafy green consumption rose 9
percent over the prior decade, but foodborne diseases outbreaks
increased by 39 percent.

"Consumption is probably playing some role but it can't
explain all of the increase in these leafy green outbreaks,"
Lynch said.

While some outbreaks can be traced to a local food
preparation source, many are widespread, suggesting a problem
in farm processing or at the processing plant," Lynch said.